Condensation of carbonyl compounds in presence of an organic heterocyclic compound having at least one six-membered ring containing three conjugated double bonds and containing boron as a hetero atom



United States Patent 01 3,520,936 Patented July 21, 1970 ice 3,520,936CONDENSATION OF CARBONYL COMPOUNDS IN PRESENCE OF AN ORGANICHETEROCYCLIC COMPOUND HAVING AT LEAST ONE SIX-MEM- BERED RING CONTAININGTHREE CONJU- GATED DOUBLE BONDS AND CONTAINING BORON AS A HETERO ATOMRobert D. Oifenhauer, Pennington, N.J., assignor to Mobil OilCorporation, a corporation of New York No Drawing. Filed Dec. 14, 1966,Ser. No. 601,807 Int. Cl. C07c 45/00 US. Cl. 260-601 1 Claim Thisinvention relates to the condensation of carbonyl group-containingcompounds in the presence of a catalyst comprising a boron-containingheteroaromatic compound having a hydroxy group attached to the boronatom. It is characterized by the substantially quantitative conversionsobtainable.

Essentially the invention comprises reacting a carbonyl groupcntainingcompound with itself or with another carbonyl group-containing compoundin the presence of the boron-containing. heteroaromatic. The boron atom,and also either an oxygen or a nitrogen atom or both, are present in asix-membered ring of the heteroaromatic as hetero atoms, and asdescribed, a hydroxy group is attached to the boron.

The useful boron compounds may have one or more six-membered rings.Generally there are two or more such rings, which are condensedtogether, one of which usually contains the hetero atoms and the otheror others of which are usually purely aromatic and may or may notcontain other substituents. However, some of the compounds may have twoheteroaromatic rings.

One of the simplest compounds has the structure IYIH BOH (l2-hydroxy-2,l-borazarobenzene Other illustrative compounds are thefollowing:

( 2) hydroxy-2, l-borazaronaphthalene (3) 2 (3(l-hydroxy-1,2-boroxaronaphthyl))benzene boronic acid (4)l0-hydroxy-10,9-borazaroanthracene (5 1 O-hydroxy- 10,9-borazarophenanthrene (6) IO-hydroxy-10,9-boroxarophenanthrene (7)2,6,8 tribromo hydroxy-10,9-boroxarophenanthrene (8)6,8-dibromo-10-hydroxyd0,9-boroxarophenanthrene (9)9-ethyl-10-hydroxy-10,9-borazarophenanthrene 10) 6,8 dichloro 1O hydroxy10,9 borazarophenanthrene (l1) 2,6,8 trichlorolO-hydroxy-l0,9=borazarophenanthrene l 2) S-nitro-lO-hydroxy-10,9-borazarophenanthrene l 3)6-nitro-10-hydroxy-l0,9-borazarophenanthrene l4)6amino-10-hydroxy-10,9-borazarophenanthrene l S)8-amino-10-hydroxy-10,9-borazarophenanthrene l6)6,8-diacetyl-10-hydroxy-10,9-borazarophenanthrene Z7)6-acetyl-10-hydroxy-10,9-borazarophenanthrene l 8)6-hydroxy-6,5-boroxarobenz(a) anthracene (19) 5,12. dihydroxy 5,12dibora 6,13 dioxarodibenz(a,h)-anthracene (20)4-hydroxy-4,3-boroxaroisoquinoline (21) Z-acetamidobenzene-1,4-diboronicacid monoanhydride (22) Z-ureidobenzene-1,4-diboronic acid monoanhydride(23) Z-acetamidobenzeneboronic acid anhydride (24)2-benzoylaminophenylboric acid semianhydride.

The preparation of several of the foregoing compounds may be indicatedbriefly for illustrative purposes. Thus, No. 6 is formed by treatment ofNo. 5 with nitrous acid followed by adding. the resulting material tohot water to give No. 6. See Dewar et al., Tetrahedron Letters, No.14-21 (1959); Dewar et al., J. Chem. Soc., 1344 (1960); Dewar et al., J.Chem. Soc., 2201 (1963). No. 20 is made by treatment of o--(CHO)C H(B(OH) with 85% hydroxylamine; see Snyder et al., J.A.C.S. -835 (1958).Preparation of Nos. 3 and 6 are described in the first two citations.No. 4 is described in Davidsonet al., J. Chem. Soc., 191 (1960).

Most of the foregoing compounds are solids at ambient temperatures. Manyexhibit physical properties, such as appearance, odor, melting point,solubility, etc., which are similar to those of the hydrocarbon whichthey structurally resemble. Chemically, they are usually stable againstoxidation by air. In several respects they have an aromatic character.For use as catalysts in the invention, they are employed in smallamounts as is customary with catalysts in general. Preferably they aredissolved in an inert solvent, which may be chosen from those known todissolve the corresponding hydrocarbon; preferably, too, a solvent ischosen which will also dissolve the reactants. For example, suitablesolvents include aromatics like benzene, toluene, the xylenes,ethylbenzene, dibutyl ether, nitrobenzene, etc.

The carbonyl-containing. compound is preferably an aldehyde or a ketone.Either may be reacted with itself, or with a compound of the samehomologous series, or with a compound of the other homologous series.The reaction of an aldehyde with itself is, of course, the familiaraldol condensation, one aldehyde molecule supplying the carbonyl groupand the other an alpha hydrogen, the product being a beta-hydroxyaldehyde, sometimes termed an aldol; if the latter contains an alphahydrogen, as according to the invention is the case, it readily loseswater to form an alpha, beta unsaturated aldehyde. The reaction may beillustrated as follows:

2RCH2CHO RCHaC-(J CHO RCHzOH=(l3 CHO H2O OH R R where R may be alkyl orhydrogen. The aldol product loses water and is convertedto theunsaturated aldehyde in the same reaction mixture. Ketones also exhibitthe aldol condensation, reacting with themselves to give a hydroxyketone which, if it contains an alpha hydrogen, as according to theinvention is the case, can lose water to form an unsaturated ketone. Thereaction may be illustrated as follows:

Where R may be alkyl or hydrogen. An aldehyde may also react with aketone, giving a hydroxy ketone which, if it has alpha hydrogen, as isthe case, may lose water to form an unsaturated ketone. Thus, thereaction may be written as follows:

The preferred reaction is that of an aldehyde with itself, or of aketone with itself. In either case, the reactant should have 2 to 3hydrogen atoms connected to the carbon next to the carbonyl group; andpreferably the resulting aldol product has an alpha hydrogen, asdescribed. The foregoing holds true when an aldehyde is reacted withanother and different aldehyde, or when a ketone is reacted with anotherand diiferent ketone. In reactions between an aldehyde and a ketone, atleast one reactant should have 2 to 3 H atoms on the carbon next to thecarbonyl; the other reactant may or may not contain these particular Hatoms.

Suitable specific aldehydes include, preferably, straight or branchedchain alkanals having 1 to 18 carbons, more broadly 1 to 22 carbons, andderived from primary or secondary alcohols. Preferred alkanals are thosewhich are liquid at ambient temperatures and pressures, such aspropanal, butanal, pentanal, 3-methylbutanal, heptanal, octanal,decanal, etc. The invention also contemplates aldehydes like methanal,ethanal, and also normally solid alkanals like dodecanal, tetradecanal,hexadecanal, octadecanal, etc. Also aromatic aldehydes likebenzaldehyde, for reaction with a reactant having alpha H atoms; alsoaralkanals like omega-phenylbutanal, omega-phenylethanal, etc. Thealdehyde may be unsaturated at positions remote from the carbonyl group.

Preferred ketones may have 3 to 20 or 30 or more carbons, and at leastone of the carbons attached to the carbonyl group should have 2 to 3 Hatoms. Normally liquid ketones are preferred, such as acetone,2-butanone, 3-methyl-2-butanone, 2-pentanone, 3-pentanone, 2-hexanone,etc. Also useful are normally solid ketones like cholestanone,androsterone, estrone, etc. Also, aromatic ketones like acetophenone,desoxybenzoin, l-isobutyronaphthone, etc.; and cycloalkanones likecyclohexanone; and ketones like 1-(2'-furyl)-butanone. The ketone mayhave unsaturation at locations remote from the carbonyl group.

The condensations, which, aside from the use of the present catalysts,are conventional, may be carried out at conventional temperatures,pressures, concentrations, and times. Refluxing temperatures arepreferred, as well as ambient pressures. Equimolar concentrationsgenerally are used when the reactants are dilferent. Reaction timesextend from 0.5 to to 50 hours or more. During refluxing, the aldolproduct loses water, as described, being converted to the unsaturatedmaterial, and this may be carried out by conventional procedures, as bydistillation, crystallization, solvent extraction, etc. Suitably thewater is allowed to distill out as the reaction proceeds, this stepbeing useful when water is the lowest boiling component and does notform an azetrope with any other component. If desired, an inert sweepgas, such as nitrogen, methane, ethane, helium, and the like, may beemployed during the reaction to help remove water.

Another preferred step comprises adding an azeotroping agent to thereaction mixture to .form an azeotrope with the water which will distillout at a temperature lower than the boiling point of any othercomponent. This step is of value in any case where it is desired tofacilitate removal of water and/or to remove it completely; it is ofparticular value when one or more of the other components is of suchvolatility as to distill over in the absence of the azeotrope.Conventional azeotroping agents are useful, including hydrocarbons likebenzene, toluene, xylene, naphtha, and agents like dibutyl ether.

Also serviceable is the use of a water trap, such as a Dean-Stark trap,which permits water leaving the reaction mixture to be condensed andremoved from the system without interfering with the condensation andreturn of any other component, including solvents.

Another water removal step comprises adding to the reaction mixture awater-soluble solvent, or a watersoluble reactant like acetone, methylethyl ketone, diethyl ketone, acetaldehyde, etc., and distilling theresulting solution from the mixture, this solution containing the waterformed in the reaction. Such solvent or reactant may be dried andreused.

Another method of removing water comprises adding to the reactionmixture, in stoichiometric amount, an anhydride of the heteroaromaticboron compound which is being used as the catalyst. Thus, if thecatalyst is 10- hydroxy 10,9 boroxarophenanthrene, the anhydride wouldbe bis(10,9-boroxaro-IO-phenanthryl) ether.

-It is desirable to add a solvent to the reaction mixture to maintainthe reactants in good contact with each other and with the catalyst.Suitable solvents are aromatics hydrocarbons like benzene, toluene, thexylenes, ethylbenzene and the like. Compounds like benzene and tolueneare specially suitable as they also function as azeotroping agents.Other solvents are ligroin, ether, chloroform, carbon tetrachloride,various chlorinated ethanes, etc.

A substantially quantitative conversion is obtainable, with yields ofunsaturated product ranging from to based on the carbonyl reactant. Itwill be understood that products like alpha, beta unsaturated aldehydes,unsaturated aldehydes, and unsaturated ketones are valuable inthemselves, as for example, plasticizers, and for conversion to othercompounds of value.

The invention may be illustrated by the following example.

EXAMPLE N-heptanal was condensed with itself in the following way. Amixture of 3.8 g. of heptanal, 10 g. of m-xylene as solvent, and 0.5 g.of l0-hydroxy-10,9-boroxarophenanthrene was refluxed, using a Dean-Starktrap. After 12 hours, the heptanal was quantitatively converted to 2-pentyl-2-nonena'l. This product was identified by showing it to have aninfrared analysis identical to a material known to be2-pentyl-2-nonenal.

It will be understood that the invention is capable of obviousvariations without departing from its scope.

In the light of the foregoing description, the following is claimed.

I claim:

1. Method of reacting an alkanal with the same or different alkanal toform a condensation product and water, said alkanals containing from oneto twenty-two carbon atoms and one of said alkanals having from 2 to 3alpha hydrogen atoms connected to a carbon atom alpha to the carbonylgroup, which comprises carrying out said reaction in the presence of acondensation catalyst comprising 10-hydroxy-l0,9-boroxarophenanthrene,said condensation product being an unsaturated alkanal of highermolecular weight than either of said alkanal reactants.

References Cited Letsinger, Chemical Abstracts, vol. 60; col. 10705,April 1964.

LEON ZITVER, Primary Examiner R. H. LILES, Assistant Examiner US. Cl.X.R.

1. METHOD OF REACTING AN ALKANAL WITH THE SAME OR DIFFERENT ALKANAL TOFORM A CONDENSATION PRODUCT AND WATER, SAID ALKANALS CONTAINING FROM ONETO TWENTY-ONE CARBON ATOMS AND ONE OF SAID ALKANALS HAVING FROM 2 TO 3ALPHA HYDROGEN ATOMS CONNECTED TO A CARBON ATOM ALPHA TO THE CARBONYLGROUP, WHICH COMPRISES CARRYING OUT SAID REACTION IN THE PRESENCE OF ACONDENSATION CATALYST COMPRISING 10-HYDROXY-10,9-BOROXAROPHENANTHRENE,SAID CONDENSATION PRODUCT BEING AN UNSATURATED ALKANAL OF HIGHERMOLECULAR WEIGHT THAN EITHER OF SAID ALKANAL REACTANTS.